Line of Police Cars on Southwest Freeway?

Today I was driving home from school and there was a line of police cars blocking traffic with their lights on, on southwest freeway. After a while of sitting there they started slowly driving like 10mph up the freeway and at each exit one would exit and block the next oncoming ramp. There wasn’t an accident or anything on the road so I’m not sure why they did this

Anyone have info? Couldn’t find anything online